Synthesis and structures of new ternary aluminum chalcogenides: LiAlSe2, alpha-LiAlTe2, and beta-LiAlTe2.

The synthesis and crystal structures of new ternary aluminum chalcogenides, LiAlSe2, alpha-LiAlTe2, and beta-LiAlTe2, are reported. These compounds are synthesized by solid-state reaction at 800 degrees C. The single-crystal X-ray structures of these compounds have been determined. LiAlSe2: a = 68228(9) A, b = 8266(1) A, c = 65236(7) A, Pna2(1) (No 33, Z = 4) alpha-LiAlTe2: a = 65317(4) A, c = 116904(9) A, I42d (No 122, Z = 4) beta-LiAlTe2: a = 44810(6) A, c = 7096(1) A, P3m1 (No 156, Z = 1). These ternary compounds are formed by fusion of AlQ4 (Q = Se, Te) tetrahedra. LiAlSe2 shows beta-NaFeO2 structure type, which can be viewed as a wurtzite superstructure. alpha-LiAlTe2 adopts chalcopyrite structure type. In LiAlSe2 and alpha-LiAlTe2, AlQ4 (Q = Se, Te) tetrahedra share four corners to build three-dimensional structures and Li atoms are located in the tetrahedral sites between the chalcogen layers. beta-LiAlTe2 has polar layers formed by three-corner shared AlTe4 tetrahedra, and Li cations are in the distorted antiprisms between the layers. 7Li MAS NMR studies show that chemical shifts of Li in these ternary chalcogenides are nearly identical regardless of different chemical environments.